In cases of chronic kidney failure, various methods of extra-corporeal blood treatment or cleansing are used to remove substances that need to be excreted and to withdraw fluids. In hemodialysis, the patient's blood is cleaned outside the body in a dialyzer. The dialyzer has a blood chamber and a dialysis-fluid chamber which are separated by a semi-permeable membrane. During the treatment the patient's blood flows through the blood chamber. To allow the blood to be cleansed effectively of substances that need to be excreted, there is a continuous flow of fresh dialysis fluid through the dialysis-fluid chamber.
Whereas in hemodialysis (HD) the transport of low-molecular substances through the membrane of the dialyzer is determined in essence by the differences in concentration between the dialysis fluid and the blood (diffusion), in hemofiltration (HF) substances dissolved in the water of the plasma, and in particular substances of fairly high molecular weight, are effectively removed by a high flow of fluid through the membrane of the dialyzer (convection). A combination of the two methods is called hemodiafiltration (HDF).
In dialysis patients, what often occur in addition to kidney failure are accompanying conditions, one of which, in a third of all cases, is diabetes mellitus. To minimize any further damaging sequelae, it is necessary for the therapy for the diabetes to be optimally adjusted. Diagnosis of diabetes mellitus and the monitoring of the therapy are performed by measuring blood sugar (blood glucose).
Both invasive and non-invasive methods of measuring blood glucose are known. Known non-invasive methods of determining blood glucose are based on measurement of the transmission of light in the patient's blood. In the infrared region, the absorption bands of glucose are at 760 nm, 920 nm and 1000 nm. However, the absorptions are so small as to be scarcely detectable. Use is therefore made of what is referred to as artificial blood kinetics.
What is used in the known non-invasive methods to measure the concentration of glucose in the patient's blood is a measuring set-up that has a pressure cuff that is applied to the patient's finger, the pressure cuff having a light source, and optical sensors for measuring transmission. A pressure that is above the systolic pressure is applied briefly to the pressure cuff on the patient's finger and the flow of blood in the finger is thus stopped, by which means what are referred to as artificial blood kinetics are produced. The red blood corpuscles collect together in groups and there is thus an increase in the size of the scattering bodies. It is possible in this way for the concentration of glucose in the blood to be determined on the basis of a measurement of transmission.
The known methods of measurement make provision for the individual measured results to be analyzed in different ways. However, what all the methods of measurement have in common is that a measurement of transmission is made at the patient's finger while pressure is being applied to the patient's finger with a pressure cuff to produce artificial blood kinetics.
The methods described above of measuring the concentration of glucose in blood are described in detail in for example the article entitled “Ilya Fine, et al: Occlusion Spectroscopy as a New Paradigm for Non-Invasive Blood Measurement, Proceedings of SPIE, Vol. 4263, pp. 122-130, 2001”. The known methods of measurement for measuring glucose concentration are also described in detail in WO 2006/006153 A1 , WO 2007/020647 A1 and WO 2004/105596 A1.
WO 2004/105596 A1 describes a method of measuring glucose concentration in which the blood flow in a finger is stopped by a first pressure cuff and the blood flow in the fingertip is modulated by a second pressure cuff which is arranged between the first cuff and the fingertip. Artificial blood kinetics are produced by this means in the fingertip and these effect the measurement of transmission and are used to allow the hemoglobin value to be calculated.
A method of determining the concentration of glucose in a dialysis fluid during a dialysis treatment is known from EP 1 083 948 B1. However, it is a precondition of this known method that a sample of dialysis fluid be taken during the dialysis treatment.
The known methods of measuring glucose have proved successful in practice. However, it is a disadvantage that a pressure cuff has to be fitted to the patient's finger or that a sample has to be taken.